1. Field of the Invention
The present invention related to a control apparatus for a hybrid vehicle having a combustion engine and an electric motor and in particular, to a control apparatus for a hybrid vehicle that adjusts the amount of energy charged by the motor, depending on a degree of throttle opening when the vehicle is cruising.
2. Description of the Related Art
Conventionally, hybrid vehicles which have electric motors as power sources for driving the vehicles in addition to engines are known.
In the conventional hybrid vehicles, there are parallel hybrid vehicles which use motors as assisting driving sources for assisting the output from the engines. Parallel hybrid vehicles assist the output from the engine by the motor when the vehicle accelerates, charge the battery by deceleration regeneration when the vehicle decelerates, and perform various controls, to respond the driver""s demands while maintaining the remaining charge of the battery (as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 7-123509).
According to the control apparatus for the hybrid vehicle using the conventional technique, in a cruise mode in which the vehicle is traveling by the driving force produced by the engine without assistance by the motor, when a target energy amount to be charged in the battery is high so that the control for using the motor as a generator is preferred, the frequency of assisting the output from the engine by the motor decreases, and the driver may therefore depress the accelerator pedal.
Particularly, in the cruise mode on a sloping road, when the control for using the motor as a generator is preferred, the driveability may be degraded, contrary to the driver""s expectation, and this may increase the frequency of depressing the accelerator pedal.
Thus, there is the problem that the driveability is degraded while the fuel consumption may be increased because the frequency of stopping the fuel supply is decreased.
It is therefore an object of the present invention to provide a control apparatus for a hybrid vehicle which adjusts the amount of energy charged by the motor, depending on the degree (extent, or state) of throttle opening, to control the driving conditions of the vehicle according to the driver""s expectations, thereby reducing the fuel consumption.
In a first aspect of the present invention, the control apparatus is provided in a hybrid vehicle with a combustion engine (E) for outputting a driving force, an electric motor (M) for generating a force for assisting the output from the engine, depending on a driving condition, a power storage unit (22) for storing electric energy generated by the motor acting as a generator using the output from the engine and electric energy regenerated by the motor when the vehicle decelerates. The control apparatus comprises: an output assistance determining device (S122, S135) for determining whether to assist the output from the engine by the motor; a generation controller (11) for setting the amount of generation (CRSRGN) by the motor and performing the generation by the motor when the output assistance determining device determines that the motor is not to assist the output from the engine; and a generation limiter (S362) for limiting the amount of generation set by the generation controller.
According to the control system for the hybrid vehicle even when the control for using the motor as a generator is preferred, the generation amount limiter limits the amount of generation, thereby providing the driving conditions responsive to the driver, and decreases the frequency of depressing the accelerator pedal, thereby reducing the fuel consumption.
In a second aspect of the present invention, the generation limiter limits the generation, depending on the degree of throttle opening (THEM).
According to the second aspect of the present invention, when the degree of the throttle opening is greater than a predetermined value, it is determined that the driver wishes to maintain or improve the driveability of the vehicle, and the amount of generation by the motor is limited, depending on the degree of the throttle opening. Thus, the motor assists the output from the engine only when the assistance is required, while decreasing the frequency of depressing the accelerator pedal, thereby reducing the fuel consumption.
In a third aspect of the present invention, the control apparatus for a hybrid vehicle further comprises a generation amount corrector (S351, S353) for correcting the amount of generation set by the generation controller, depending on the driving conditions of the vehicle. The generation limiter limits the corrected value of the amount of generation.
According to the third aspect of the present invention, the amount of generation is corrected, based on the remaining battery charge, the operation of the air conditioner, and the electric current consumed by various electrical devices.
In a fourth aspect of the present invention, the control apparatus for a hybrid vehicle comprises: a mode determining device for determining at least one of an acceleration mode, a cruise mode, and a deceleration mode, depending on the driving condition of the vehicle; a generation controller (11) for directing the motor to generate electric energy without the assistance of the output from the engine when the mode determining device determines that the vehicle is in the cruise mode; and a generation limiter (S362) for limiting the amount of generation, depending on the driving condition of the vehicle. The motor generates the electric energy, based on the amount of generation limited by the generation limiter.
When the vehicle is in the cruise mode in which the assistance of the output from the engine is not required, and when the load on the engine is high, e.g., when the vehicle is cruising on an uphill road, the load on the engine arising from the generation is decreased. Therefore, the degradation of the driveability of the vehicle is prevented, and the frequency of depressing the accelerator pedal can be decreased, thereby reducing the fuel consumption.
The control apparatus for a hybrid vehicle further comprises a remaining battery charge measuring device (13) for measuring the remaining battery charge. When the remaining battery charge is below a predetermined value, the generation limiter does not limit the amount of generation.